In my U.S. Pat. No. 3,708,296 referred to hereinabove, there are disclosed epoxide-containing materials which are photopolymerizable via use of organic compounds which are radiation-sensitive and release an active catalyst upon exposure to electromagnetic radiation. It has now been discovered that the novel radiation-sensitive catalyst precursors disclosed and claimed therein are effective to initiate photopolymerization of another class of related cyclic monomeric materials, namely lactones, and mixtures thereof with other materials polymerizable through the action of such catalyst precursors such as epoxides.
The invention more specifically relates to polymerizable compositions comprising mixtures of a monomeric lactone with monomeric or prepolymeric epoxides and radiation-sensitive aromatic diazonium salts of complex halogenides and process for polymerization of such compositions.
To effect polymerization of the above defined monomers, it is believed to be necessary to open the ring of the monomer through cleavage of the carbon-oxygen bond. A reactive intermediate is formed which can subsequently open up another lactone and epoxide ring and this reaction may repeat itself many times in a chain reaction to form a polymer of repeating ester and ether units.
Previously, isolated instances have been reported in the literature wherein lactones have been polymerized by the action of electromagnetic radiation. This can be achieved by selecting a region of the electromagnetic spectrum to which the monomer responds to form an initiating species that causes the polymer chain to grow. For example, Hayashi et al in Die Makromolekulare Chemie, pp. 230-237 (1961) have reported that gamma radiation will effect polymerization of propiolactone. However, this type of reaction has not been believed to be generally applicable to most lactones and additionally gamma radiation is not a convenient source of radiation and is not as useful as the ultraviolet and visible regions of the spectrum. Therefore, heretofore polymerization of lactones has been carried out by heating the monomer in which a chemical compound was incorporated until catalysts contained therein were activated, for example, as disclosed in U.S. Pat. No. 3,371,965. The activation of the catalyst upon heating thereby initiated polymerization of the various monomers. These methods, though successful, are unsatisfactory in that careful attention must be given to staying within the temperature limitations of the system involved. In order to prevent the harmful effects of heat curing, it is often necessary to extend the curing cycle an unreasonable length of time. Many of the prior art aryl diazonium salts, for example, perchlorates are explosively hazardous and tend to be chemically unstable. Furthermore, unexpectedly, it has been discovered that the catalyst activity and resulting usefulness of aryldiazonium compounds cannot be determined on a random basis. Moreover, it has been unexpectedly discovered that many aryldiazonium compounds do not possess the requisite properties necessary to catalyze the wide variety of monomeric polymerizable materials of this invention. Accordingly, it is desirable to identify new and improved catalyzing agents useful in the photopolymerization of lactones which are not subject to and overcome the deficiencies now existing in the art.